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AT Command Set
This document details many of the AT commands implemented by various modems. Keep in
mind that not all modems use these commands or use these commands in the same way.
AT - Command Prefix
A - Auto Answer
A/ - Re-executes The Last Issued Command
Dn - Dial A Number
DL - Dial The Number Most Recently Dialed
DSn - Dial A Phone Number Stored In The Directory
En - Set The Local Echo
Fn - Set The On-Line Echo
Hn - Takes The Modem On/Off Hook
In - Returns Information About The Modem
Ln - Sets Speaker Volume
Mn - Sets Speaker On/Off
On - Return To On-Line Data Mode
P - Set Pulse Dialing Default
Qn - Enables/Disables Result Codes
Sn - Read - Write - Display S Register
T - Set Tone Dialing Default
Vn - Set Verbal/Numeric Result Codes
Xn - Set The Result Codes To Be Displayed
Zn - Reset The Modem
&Cn - Controls The Carrier Detect Signal (CD)
&Dn - Controls The Data Terminal Ready Operations (DTR)
&Fn - Restore The Factory Configuration(s)
Required to begin all other commands except A/ and +++.
Can be used alone to test for an OK result code.
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Enter auto-answer mode. Modem goes off-hook at attempts to answer incomming calls.
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Re-executes that last issued command. Does not require the AT prefix.
to re-dial the last dialed number
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The following modifiers are allowed:
P - Use pulse (rotary) dialing.
T - Use tone dialing.
, - Two second pause.
; - Return to Command mode after dialing.
! - Flashes the switch hook.
/ - Delays for 25msec. before dialing.
W - Wait for dial tone.
@ - Wait for five sec. of silence before continuing.
# - The pound or gate digit. Used in tone dialing.
* - The star digit. Used in tone dialing.
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What the title implies.
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DSn - Dial A Phone Number Stored In The Directory
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E0 - Echo Off.
E1 - Echo On.
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Fn - Set The On-Line Echo
Hn - Takes The Modem On/Off Hook
In - Returns Information About The Modem
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L0 - Low
L1 - Low
L2 - Medium
L3 - High
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M0 - Speaker always off.
M1 - Speaker on until connect.
M2 - Speaker always on.
M3 - Speaker on after dial, until connect.
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On - Return To On-Line Data Mode
P - Set Pulse Dialing Default
Qn - Enables/Disables Result Codes
Sn - Read - Write - Display S Register
T - Set Tone Dialing Default
Vn - Set Verbal/Numeric Result Codes
Xn - Set The Result Codes To Be Displayed
Zn - Reset The Modem
&Cn - Controls The Carrier Detect Signal (CD)
&Dn - Controls The Data Terminal Ready Operations (DTR)
&Fn - Restore The Factory Configuration(s)